1. Field of the Invention
This invention relates to guided projectiles that engage targets by detecting and following laser light scattered from the targets, and more particularly to angle measurement for a wide field-of-view (WFOV) semi-active laser (SAL) seeker.
2. Description of the Related Art
Laser guided ordinance is commonly used to engage point targets with a high probability of success and minimal collateral damage. Such ordinance includes guided artillery projectiles, guided missiles, and guided bombs, all of which will be referred to herein as “projectiles”.
A laser guided projectile's guidance system typically includes a semi-active laser (SAL) seeker to detect pulsed laser electro-magnetic radiation (EMR) scattered from the intended target and to provide signals indicative of the target bearing and a flight controller that processes the signals to manipulate one or more control surfaces (e.g. fins or canards) to guide the projectile to the target. The SAL seeker includes a non-imaging optical system that captures and focuses the scattered laser EMR into a spot onto a segmented non-imaging detector (e.g. a quad-cell detector). As the target bearing changes the position of the spot on the detector changes. The detector compares the integrated EMR incident on each cell (segment) to calculate a spatial displacement of the centroid of the spot. The effective field-of-view (FOV) is dictated by the central monotonic region of the detector's spatial transfer function (STF) in which the spot is incident on all four cells, which is in turn determined by the spot size. The detector's central monotonic region is commonly referred to as the “linear” region.